Apparatus for heating oil wells



July 28, 1953 c. A. CARPENTER ETAL 2,647,196

APPARATUS FOR HEATING OIL WELLS Filed NOV. 6, 1950 Illini Patented July 28, 1953 APPARATUS FOR HEATING OIL'W-EILLS Clayton A; Carpenter, Wilmington, and Richard S. Crog,Los Angeles, Calif., assignors .to-Union @il Company of: California, Los Angeles, Calif., a corporation of. California ApplioationfNovember 6, 1950, vSeriaLN 01.-.194370 f2 This invention lrelates fte; an .apparatusor heating Aoil Wells whereby the. vrate. of. oil flow and-the vnet yield Aof oilcanbe increased.H More particularlyfthis invention relates to anappara-V tus for thevsimultaneous Vheating and pumping of oil Wells.

Many ymethoclshave been employed in the prior art 'for heating oil ,wells such as by electrical means, injecting heat transfer agents into the Well suchas steam, hot oils, etc. and by burning naturalgas in they well bore.Y In general 'such methods have met with little or no commercial successeur-1in part to the low eliciency of the apparatusemployed and to the relatively large amounts: of energy vthat-were required to operate such equipment.

It 'is an object of vthis invention to provide annelectric heater for heating a limited portion of an oil-bearing formation `surrounding en oil Well borevvhereina highly Veilicient mode of heat distribution is employed.

It is another object of this invention to provide a unitary electricalheater which is readily assembled and which requires a lminimum of maintenance. y

It isanother object-of this invention to. providelan electric heater forheating oil wells which is easily run in and .ou-ton the .tubi-ng of :a con.- ventional well and wherein a minimumnoipreparation. .is:;required to.install V.the heater in a conventional A,existing well..k

Itis another object of thisfinventionto .pro- Vide an electric `heater ioroil Wells of a unitary construction` wherein there lis a maximum trans-vk fer-...of heataWay fromv the longitudinalaxis of theheaterand a minimum transfer ofheatfto- Ward the: oil flowing lalong, the longitudinal axis.

It-.isanother 'object of this inventionto .provide ay'vvell heater comprising a spring-loaded mechanism tor compensating. for differential ex. pensioni-of:y one membergof'the heater. relative to a second member.

Other objeotsoi this invention will `become ap.- parentxtothose skilled. in the art as the-.descrip-V tion thereof. proceeds. y

Ir1:general', .the `present, invention relates. to.. a new-electric heater for oil-*wells which is oifa russedjunitary "construction-.f- In theI oilI well heaters oiltheprior lart considerable diiculty hasfbeen experiencedin maintaining the :heater huid-.tight to preventthe entry of the bore .hole fluidsintoi contact. with .the heatingielements; Oil Wellf'lbrinewacauses .severe corrosion not. `any\ o-i the.. exposed-fittin-gsrand; often :produceswshort cir- .cuiting .oigtha 4entirewheateu.;4` The heater:` ofl this invention 'is carried on .the .tubing and is. easily'.

run. inzor. outwith only. minoradaptation of the existingaequipmento Electricalenergy is supplied to the heater through .a...fsing`lefinsulated cable. and is returned through a grounded connection to the metalpartsA of the tubing. The yheater mountingis attached-to the. .pump and the core of thegheatingr unit` is. aoentral oil conducting pipe-Which servesthe function of a Skeeter bill!! Above the .heater .mounting in the tubing `string isa pump shoe-lockwhich accepts a conventional pump shoe and retains. the pump above the heater in a semi-.rigid position. The .pump takessuction' on apipe coaxially .disposed and passing down- Wardly throughlthe. .heating .elementflto below Removal oi the .liquid level.jin,the..hore hole. the Iheater iseiiected by ,removing the rods-and pumpin a conventional lmanner and Withdrawr` ing the tubing uponiwhich theheater 'is carried;

Figure 1 shows a partly kcross-sectional viewof anoilwellwherein an electric heater of this ine vention isemployed for the simultaneous heating-pumping of a yWell and wherein the surface of the Aoilpoolis maintained somewhat below| l the bottom of. theh'eate'r. in the oil sand to permit a major portion of the heattol be transferred from. the. heater. through the. gaseous .phaseabovc the liquid leveloiY the pool. The feature of transferringheat yfromV the heater toA .the `formation surrounding the bore `via an intervening gaseous phaserather than .via the pool of liquid. oil forms no part ofthel present. invention but is disclosed' and claimed in my copending application Serialv No..17.7,926,.nlled August 5,1950.

FigureaZ showsa partial cross-sectional view ofthe heater. assembly of this invention 'together with .thecentral'pipe Which serves as the Skeeter billf! Figure 3 shows a Apartial cross-sectional elevation Vview otameans for passing theinsulateu electricalfconductor through a suitable seal to prevent entry ,.of. `oil into the heater proper and to-protect the electricalconductorirom the high ambient .temperatures surrounding the heater.`

Figure. .4 showsacrossesection of Figure 2 through the plane 4 4. f

Referring. now .more particularly to Figure l, well casing H extends downwardlyirom ieartli surface it into bore .hole Il tov the vicinity ,of the upper boundary of. oilfbearing sand lil; well casing :Il isoapped .with tubing head 551 Tubing' i6 .issuspentledthrough.. .tubing head i5l and passes downwardly. ythrough casing i. Tubing .I isvfittedivwith .coupling il. to which attached p pum-plooi; shoeA I9.. Atthe earthsuriace tubing 3 i5 is fitted with stuffing box 2| and stuffing ring 22 through which sucker rod 23 is permitted to reciprocate. Sucker rod 23 iS attached to a rod hanger and walking beam assembly not shown.

Within tubing I6 and attached to sucker rod 23 is pump 25 which is attached at the lower end to pump lock 28 insertable in and normally retained by pump lock shoe I9. Heater unit 28 is suspended on Skeeter bill 29 which is threaded into the lower section of pump lock shoe I9. At the lower end of heater 28 the Skeeter bill unit is fitted with coupling 3| which is in turn attached to perforated section 32 which is submerged below the liquid level of oil pool 33 in the bottom of bore hole |3.

Alternating current generator 48 at the earth Surface generates an alternating current which iiows through one lead 4| to a grounded connection at tubing hanger I5. The other line 42 from the alternating current generator 48 passes through a suitable packing gland 43 into normal gas production line 44 and thence to electric heater unit 28. The return element of heater 28 is grounded to Skeeter bill 29.

Referring now more particularly to Figure 2 which shows a partial cross-sectional view of heater unit 28, Skeeter bill 29 traverses the entire length of the heater unit and is an integral part thereof. The lower closure member 58 is welded to Skeeter bill 29 at weld 5| which provides a circular seal around the Skeeter bill 29. Tubular centering member 52 extends upwardly from an upper shelf of member 58 and coaxially with Skeeter bill 29. Tubular aligning or centering member 52 is supported on member 58 by suitable welds 53. Upwardly from the lower member 58, tubular centering member 52 is maintained in coaxially alignment by supporting member 54 which is in turn welded to Skeeter bill 29 by weld 55. Supporting member 54 slidably contacts the inner surface of tubular member 52 thereby permitting expansion or contraction of the tubular member relative to Skeeter bill 29. Springs 56 press on their lower side against lower member 58 and on their upper side against tubular member 58.

Eerforated disc 88 presses against the upper end of tubular member 58 and opposes the force of springs 58 attempting to push tubular member 58 upwardly. Perforated disc 88 is anchored to Skeeter bill 29 by suitable Welds 62 which also provide an electrical ground connection to Skeeter bill 29.

Tubular member 58 on its outer surface is fitted with two series of spiral channels within which are wound heating coils 83. One terminal of the heating coil is grounded to perforated disc 88 by suitable contact 85. The coil grounded to contact 85 traverses one series of grooves to near the bottom of the tubular member 58 and at plug El it is transferred into the other series of grooves and winds upwardly on the face of the coil. It then passes through hole 69 in tubular member 58 and passes upwardly to the conducting cable I9 to be described hereinafter. By this method the heating coils 83 are wound non-inductively so as to minimize the electrical impedance thereof.

Somewhat above perforated disc 68 is mounted upper closure member 18 which comprises the top plate or upper closure of the heater. Closure member T8 is fitted with hole 1| which is in turn fitted with plug 12. Removal of plug 12 permits compressed air or other gas to be admitted to the inner chambers of the heater in order to test for leaks after the completion of the assembly. Member 18 is also fitted with flexible pipe 'I5 by means of nipple l1 which permits egress of electrical conductor 19 passing from hole 89 in tubular member 58.

The outer shell 88 of the heater is circularly welded to lower closure member 58 at weld 8| and is welded to upper' closure member 18 at weld 82. Welds 8| and 82 completely seal the inner chamber of the heater. Shell 88 is coated on the inner surface with a ferro-enamel layer such as is used commercially. Ferro-enamel layer 85 is firmly bonded to shell 88 and provides a nonconducting coating on the inside of the shell which prevents electrical contact between metallic shell 88 and the exposed coils 63.

Referring now more particularly to Figure 3 conductor '|9 passes upwardly through nipple attached to braided flexible pipe 75. The exposed metallic flexible joint of flexible pipe T5 is welded to inner sleeve 98 at weld 9|. Outer Sleeve 92 iits over inner sleeve 89 and is welded thereto at circular weld 93. The upper end of outer sleeve 92 fits into one end of rubber tubing 94 which is secured thereto by external clamp 85. At its upper end, rubber tubing 94 is fitted to Sealing member |88 and is secured thereto by clamp |8|. Threaded member |82 screws into the upper threaded end of sealing member |88 and the beveled face thereof compresses O ring sealing member |93 which is normally torus-shaped. Compression of O ring |83 provides a seal between insulation |84 covering conductor |85 thus preventing any possible oil fiow downwardly between sealing member |88 and insulation |84 covering conductor |85.

rl'he use of rubber tubing 94 serves to provide a junction for splicing high temperature insulated conducting wire 19 with the low tempcra` ture, general purpose insulated conductor |85 insulated by insulating sheath |84. In the usual method wire 79 is brought out of the heater 28 through nipple '.'l' and flexible pipe f5 tted with inner sleeve 98 and outer sleeve 92. The high temperature conductor is then spliced to the low temperature conductor fitted through the seal provided by sealing member |88 and rubber tubing 94 is then fitted over the splice and clamped into position.

Referring now more particularly to the method cf assembling the heated unit shown in Figure 2, the following method has been found most suitable. A pipe of suitable dimensions is selected for Skeeter bill 29 and the lower closure member 58 with a suitable opening for insertion of Skeeter bill 29 is slid over the Skeeter bill and is welded at weld 5|. Supporting disc 54 is thereafter welded to Skeeter bill 29 by weld 55 a suitable distance upwardly from lower closure member 58. Thereafter the tubular aligning member 52 is fitted into place and welded at 53 and compression springs 59 are next fitted over Skeeter bill 29 and placed in contact with lower member 58. Coil form 59 with mounted coils 83 is fitted over tubular member 52. Perforated disc 68 is fitted over Skeeter bill 29 and is pressed downwardly against coil form 58 so as to put compression springs 58 under partial compression. With compression being maintained against springs 58, weld 82 is made, thereby fastening perforated disc 68 to Skeeter bill 29. If desired, suitable transverse pins 85 may be employed to pin coil form 58 to perforated disc 68 to prevent rotation of coil form 58 relative to Skeeter bill 29. The appropriate sl sacem se 'coit'terminalyare-brought" outithroughthfperforations of perforatediiisiitz'landvmontactES is established and thev other coilfrtermial is 81| @maintain- @Compressed lug finis-trema ede-nd instailatiomiritheiwell In fthe installation of .heater 281m zitheiman- 'fist attached to the upper end of heateizfxrandithewholefis v was "producing Iaboutf'irtwelvefibarrelsif peri day@ of A538@ API 1 gravity,v highly:".parainicfacrude oil was lfs'elettedfor electric heating experiments. i When `the Well was produced without' heating-gothes'temperatureof theafoil 'poolfiwas 470.; Fsfand the "for- Hmatiorrl temperitu-ref` ylat 1 al1-point .emovedrx'from the Well# pool was-"determinedito:betlabout 84- F. The thickness of.' the"@formation'.:wasil-about 9 feet; Uponivthe'' installations..andig'operation-zot the'1 electric heater ati.r ai steady @powerAv frate. lof l onlyi'about '7: kilo-Wattsgl theirvwell :produced quite -uniformly average fof 45r barrelsiiper,.dax for a''-period of 30""days"l duringlthe.ficontinuancefiof the heating operation. "whenktheiheateri-lwas 1 :removed and the productionoff-'the WellsA was f-resumedffwithoutany heating whatsoever, the'p'ro- ^duction declinedl within a-'fweekifto foirrly'about zbarrels'perlday.

4fWhile the exact-reasons"for*the success iut-this' experimentarevv not "kno-wnff'witlr certainty; riti lis heating was merely l "stilifoientif toI-f-fovercome'flthe siti'on on* thebmehole4 iWall fof the formation.

In the particular 4'esperimenti-thetemperature According toai' preferredtlmode'i-'bf operation,

lonly a' *limited amountof 'heats'. aplied t" the 'oil-bearing"'formation .'It has` been" found vthat L heaterswperatins .at a powermlevelxof"about" 0.02am to `21T'kilowatts per" foot "oft'formationfare'most I efficient "for Waff-bearing" rvifells.

1t is no-W believed thatlthe previolus'attempts to employ 'electric' 'heating"havegenerallyf'met 116 liftelden?'a-blelaple'riod' "ofi time faiidfftlfratf'fifv itrwere' ire-- moved the well would thereafter f'cofntinuef-to' rooluoeifatA al'hilighf-lrateior a vconsiderable-period 2.lowftemperatures with f istributionfandis' preferlitoi::transferrall for4 parte '-of hegaseou's'phase'frathe than `ozthe; lreiuidgpl i 'he favorableiresultsi-attainecl a y theenpenation of.` hisiheaternare of. a type and magrills-udetambient iwerexsnot :iobtainabl e: x heretogoffiore vbyfiemployingsthermethods of the: priortart. yfr-In `the useiiof: the/:rpresentfheaten.alternating voortent; is; genera yfpreferablezzto. .d-irectrzcurrent fore-'convenience fr, ff.; handling; fand; availability. .(.E'l'ectrolytior :corrosion 'isgenerallyf greater.` when directxcurrent-i-isaemployed .1 The: `yoltagesli employedfin-thecase-fof. alternating currents are geli-.erally between'. about 10,A tol v1000k volts; anclzpref erablyf betweentaboutzto d50-Volts. 4voltages?'loe- `.tween about 5 .tofGQO; volts iandfrpreferab'ly about isof/QOVE'G 'MONS HTS 'employed inthe zcase'iof. direct ,icnrrents.

1 WithregardI-to-.the :amountlof.heat'required'zin -order ;to..sustain awhighf-ra-tejofviiovvr'from` a given .othbearingffsandt it has been found y.that usually .35..L aflieaterll operating at.. a power :ratei between 0.02

.wandkilowatts'ioff-y -powferf iper-:footfzof .formation .a:toobefiheated:,isasuitable. :.Preferably vvthe .power rate should-be between 'a'boutE 0.1:.and'..1.0 kiloiflwatts'nemfoot. The gaseous phaselaboveithe oil @Wamel-Should bewheated @at least fto .about l 25?y F.

.aboyefthe formation#temperaturesand.. thei'oilillin .the swellabore should-be :.heatedzl atszleast' about @10 F: tabove the formationftemperature. `In ;..geneiza1-f. the; gaseoustphasesshould beaheatedto k4 `@ab etvieen about; `10G.9 l E. and 290; tand :preferably ff-...toebetween 1j-30 andl80^ theoilap'ool should I, besheatedto between-.about 90 F.; l'and l160" F. and preferably-r lbetween about 110 and 11.401` F. fVl/.herethe oils is :heatedv ato higher:.ztemperatures Mconsiderable. andideleteifious.` gas-separation oc- .curssandl muchflcoke-andy 4gum 'deposits on: the ,.`eq;ipment,\ .which necessitates frequent removal.

At appreciably lower temperatures 11o-increase v`in theeproductionmate.is obtained.

3,354 reqilillesa minimum of..maintenance.` Whileother .forms-.'of;.heatsconduoting .electrical insulation ...maybe .employedpthe ferrwenamel type.;k is by .far l.the most favorable The ferro-.enamel layer .mayr :be deposited. :on 7 Qfhthe iron or steel tubeby.y any. suitable. conventional method. l"Onem'i'etl'iod consists .of .plugging oneend of the. tube, pouring it ui`ull,..or partially l`""`1`11ll,Wltl1 va suitableclayfcohtaining.ferro-.enamel 'mixtureponring'ithe mixturlfrom'.thestubeand hard ferro-enamel surface on theinside of the bore of the tube.

Another feature of this invention lies in the heat insulating barrier or barriers placed between the heating coils and the Skeeter bill. It has been found that the greatest effectiveness of a unit of heat is realized when the heat is transmitted by radiation through an intervening gaseous phase to the exposed formation face. As has been stated hereinbefore, the gaseous phase interposed between the heater and the formation face is established and maintained by controlling the rate of pumping of the liquid level in the bore hole. It has also been found that the heat otherwise transmitted through the walls of the Skeeter bill to the column of oil flowing upwardly therethrough to the pump is rapidly dissipated from the oil and contributes little to increasing the oil production of the well. In the preferred modiiication of the invention the coil form is of a heat insulating variety which transfers a minimum of heat from the heating coils to the inner surface of the coil form. Furthermore, the maintenance of dead air space between the inner face of the coil form and the Skeeter bill also serves to minimize heat transmission therebetween.

In one modification of the invention a solid heat barrier may be employed between the windings and the central pipe or skeeter bill. Referring again to Figure 2, member 52 and member 54 may be deleted and coil form 58 may be fashioned so that it fits snugly over skeeter bill 29 and extends to within a short distance of insulation liner 85. When the coil form is thusly fashioned of material having a low heat conduci tivity, the major portion of the heat generated in the coils is transferred to the tubular shell 80 and thence to the coil bearing formation.

Another feature of this invention lies in the method of mounting the coil form which is generally fashioned of a material having a low thermal rate of expansion within the metallic elements which generally have a much higher rate of thermal expansion. Thus in the preferred form for mounting the coil form within the heater the top of the coil is suitably pinned directly or indirectly to the nearby section of the Skeeter bill while the lower end of the coil form is pressed upwardly by the springs under compression, thereby maintaining a rigid mounting, Also, the use of the tubular aligning member further increases the rigidity of the coil form mounting.

Another feature of this invention lies in the use of a huid-tight unitary heater construction wherein the electric conductor is passed through a sealing means and into the heater chamber itself. The sealing means provides for a fluidtight seal between the conductor cable of the well bore and the conductor within the heater proper.

While only a single phase heater has been described hereinbefore, it is apparent that 3-phase or other polyphase heaters may be employed similarly. For three phase electric heating three coils are wound on a three coil form with the lower ends of the three coils being connected together and the upper ends being attached to the three leads from the current source. The same features of sealing, insulating, etc., may be applied thereto.

The foregoing disclosure of this invention is not to be considered as limiting since many variations may be made by those skilled in the art without departing from the spirit and the scope of the following claims.

We claim:

l. A well heating apparatus comprising a central oil-conducting conduit; an outer heat-radiating shell; an upper closure; a lower closure; said upper and lower closures providing a fluid-tight seal rbetween said conduit and said shell, and maintaining said shell coaxially disposed around and spaced away from said conduit; a tubular coil-form disposed between said shell and said conduit, said coil-form having spiral grooves cut into its outer surface to receive an electrical resistance heating coil and being formed of an electricaland heat-insulating material; a coil-form retaining member affixed to said conduit adjacent said upper closure and receiving the upper end of said coil-form; resilient means disposed between the lower end of said coil-form and said lower closure; 'an electrical resistance heating coil wound in the grooves of said coil-form; and sealing means for passing an insulated electrical conductor through the outer surface of said apparatus to said heating coil.

2. An apparatus according to claim l wherein that portion of the inner surface of the heatradiating shell which is co-extensive with the heating coil bears a heat-conducting electricallyinsulating coating.

3. A well heating apparatus comprising a central oil-conducting conduit; an outer heat-radiating shell; an upper closure; a lower closure; said upper and lower closures providing a fluid-tight seal between said conduit and said shell, and maintaining said shell coaxially disposed and spaced away from said conduit; a tubular coilform disposed between said shell and said conduit, said coil-form having spiral grooves cut into its outer surface to receive an electrical resistance heating coil and being formed of an electricaland heat-insulating material; alignment ineansaffixed to said conduit and maintaining said coil-form spaced away from said conduit and in close proximity to said shell; a coil-form retaining member affixed to said conduit adjacent said upper closure-and receiving the upper end of said coil-form; resilient means disposed between the lower end of said coil-form and said lower closure; an electrical resistance heating coil non-inductively wound in the grooves of said coil-form; andsealing means for passing an insulated electrical conductor through said upper closure to said heating coil.

4. An apparatus according to claim 3 wherein that portion of the inner surface of the heatradiating shell which is co-extensive with the heating coil bears aheat-conducting electricallyinsulating coating of ferro-enamel,

5. A well heating apparatus comprising a central oil-conducting conduit; an outer heat-radiating shell, the inner surface of which bears an electrical-insulating heat-conducting coating; an upper closure; a lower closure; said upper and lower closures providing a fluid-tight seal between said conduit and said shell, and maintaining said shell coaxially disposed around and spaced away from said conduit; a tubular aligning member having its lower end affixed to said lower closure and having its upper end slidably engaging a transverse disc-like support affixed to said conduit, said aligning member beingr coaxially disposed to `and spaced away from said conduit; a tubular coil-form disposed between said aligning member and said outer shell, said coilform having spiral grooves cut into its outer surface for receiving an electrical resistance heat- References Cited in the le of this patent ing coil and being formed of an electricaland UNITED STATES PATENTS heat-insulating material; a coil-form retaining member aixed to saidconduit and receiving the Numbers Name Date upper end of said coil-form; resilient means dis- 5 7821233 Gamme? F911 14 1905 posed between the lower end of said con-form 11171444 Qu'am Maf-"7. 1916 and said lower closure; an electric resistance heat- 1'309721 Drmkem J U15 15 1919 ing coil non-nductively wound in the grooves of 113541757 Ppcke et a1 Oct- 5, 1920 said coil-form; and sealing means for passing an 2,186,035 Nues Janf 9, 1940 insulated electrical conductor through said upper 10 244,255 1100111011 Jul-'1' 3, 1941 closure t0 said heating CoiL 2,302,774 JLI'VIS NOV. p24, 1942 CLAYTON A CARPENTER. 2,332,708 Freeman OC, 26, 1943 RICHARD s` CROG- 2,500,305 Ackley Mar. 14, 1950 2,548,360 Germain Apr. 10, 1951 

